circuit breakers for direct current applications

Circuit breakers for direct current applicationsComplementary technical information

2

Complementary technical information

Circuit breakers for direct current applicationsContents

Typical applications 3

Types of direct current networks 3

24 - 48 V direct current protection solution 4

Constraints related to "direct current" applications 6Type of load 6

Time constant 7

Tripping curves 8Example 8

Continuity of service of the solutions 9Discrimination of the direct current protection devices 9Total discrimination solutions 9Coordination with loads 11Example 11

The personal protection 12

Examples of applications 13Industrial applications 13Tertiary applications 15

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Circuit breakers for direct current applications (cont.)24 V - 48 V direct current applications

Typical applications Direct current has been used for a long time, and in many fields. It offers major advantages, in particular immunity to electrical interference. Moreover, direct-current installations are now simpler, because they benefit from the development of power supplies with electronic converters and batteries.

b Communication or measurement network: v 48 V DC switched telephone network, v 4-20 mA current loop. b Electrical supply for industrial PLCs: v PLCs and peripheral devices (24 or 48 V DC). b Auxiliary uninterruptible direct current power supply: v relays or electronic protection units for MV cubicles, v switchgear opening / closing trip units, v LV control and monitoring relays, v indicator lights, v circuit-breaker or on/off switch motor drives, v power contactor coils, v control/monitoring and supervision devices with communication that can be

powered via a separate uninterruptible power supply. b 24 to 48 V DC wind application: v isolated homes, v cottages, bungalows, mountain refuges, v pumps, street lighting, v measuring instruments, data acquisition, v telecommunication relays, v industrial applications.

Types of direct current networks According to the types of DC networks illustrated below, we can identify the risks to the installation and define the best means of protection.

For further information on the types of networks and the faults that characterise them, refer to the direct current circuit breaker (LV) selection guide, 220E2100.indd.

For all these configurations, we propose a single protection solution that depends only on the requirement for the nominal current In and the short-circuit current Isc at the installation point concerned.

The second important point in our solution is the fact that the protection is implemented by non-polarised circuit breakers that can operate efficiently, whatever the direction of the direct current.

DB

1242

36

Earthed Isolated from earthI: Earthed (or grounded) polarity (in this case negative) II: Earthed mid-point III: Isolated polarities 1 pole (1P isolation) 2 poles (2P isolation) 2 poles 2 poles

DB

1240

75 In

Un

DB

1240

67 In

Un

DB

1240

76 In

Un/2

Un/2

DB

1240

68

D

E

In

Un

2 poles (1P isolation 1P+N)

DB

1243

87 In

Un

Worst-case faultsFault A and fault B (if only one polarity is protected) Fault B Double fault A and D or C and E

Isc

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In

Un

24 - 48 V direct current protection solutionThe performance levels shown in the tables below correspond to the most critical faults according to the network configuration.

b Breaking on one pole. b Fault between polarity and earth (Fault A).

Standard solution depending on the network and the requirements of the installation (In / Isc)In addition to the parameters shown on the following pages, the tables below illustrate our range of circuit breakers according to the nominal current of the load and short-circuit current at the point of installation.

b Circuit breaker rating. b Breaking capacity of the circuit breaker.

1 pole isolation solution (1P)Breaking capacity (kA)Icu IEC 60947-2

Maximum rating (A)

y 10

y 15

y 20

y 25

y 36

y 63 y 80 y 125 u 125

y 50

iC60a C120N

C120H

iC60N

iC60H

iC60L NG125N

NG125H

NG125L

Compact NSX

y 4.5

iK60N

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DB

1243

83

DB

4064

65

5



(*) 3P NG125N connected in a two-pole configuration to reach 125 A (1P / 2P NG125 has a maximum rating of 80 A).

1 pole isolation solution (1P+N)

Specific use of the iDPN range in a network with one polarity earthed and both poles isolated: compact solution (1P+N in 18 mm).

2 pôles isolation solution (2P)Breaking capacity (kA)Icu IEC 60947-2

Maximum rating (A)

y 10

y 15

y 20

y 25

y 36

y 63 y 80 y 125 u 125

y 50

y 4.5

iC60a

iK60N

C120N

C120H

iC60N

iC60H

iC60L NG125N NG125N*

NG125H

NG125L

Compact NSX

In

Un

In

Un/2

Un/2

D

E

In

Un

y 6

y 40 y 63

iDPN N iC60a*

Breaking capacity (kA)Icu IEC 60947-2

Maximum rating (A)

(*) iC60a breaking capacity Icu = 10 kA.

In

Un

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DB

1243

84D

B12

4385

DB

1243

86D

B12

4077

DB

4064

66D

B40

4549

6



Constraints related to "direct current" applications In direct current, inductors and capacitors do not disturb the operation of the installation in steady state. Capacitors are charged and inductors no longer oppose changes in the current. However, they create transient phenomena when the circuit opens or closes, during which time the current varies. Actual loads have both characteristics and generate oscillatory phenomena.

Type of loadInductive load

An inductive load will tend to lengthen the current interrupt or establishment time, because the inductance L then opposes the change in the current (Ldi/dt). The transient phenomenon will mainly be characterised by a time constant imposed by the load and whose value corresponds approximately to the interrupt or closing time that the switchgear has to withstand. In addition, during the interrupt time, the switchgear must be able to withstand the additional energy stored in the inductor in steady state. An inductive load therefore requires particular attention with respect to its time constant. A low value (typically < 5 ms) facilitates interruption.

Capacitive loadDuring a closing operation, a capacitive load will cause an inrush current due to the load on the capacitor, virtually under short-circuit condition at the beginning of the phenomenon. On opening, it will tend to discharge. The time constant is generally very low (< 1 ms) and its effect is secondary with respect to the inrush current. A capacitive load will require particular attention to the inrush or discharge current surges.

DB

1242

40 US

i

S LRE Ri

UL = L di/dt

DB

1242

41

E/R

τ = L/R

i

t

Inductive load

DB

4045

50

i

S

CE ReqES

ULRsource + Rcables

DB

1242

43

τ =

i

i = E/Req

E

t

Rsource + Rcables

Iinrush =

Rsource CCapacitive load

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Time constant L/RWhen a short-circuit occurs across the terminals of a direct current circuit, the current increases from the operating current (< In) to the short-circuit current Isc during a time depending on the resistance R and the inductance L of the short-circuited loop.

The equation that governs the current in this loop is: U = Ri + Ldi/dt.

A short-circuit current is established (neglecting In with respect to Isc) by the equation: i = Isc (1 - exp(-t/τ)),where τ = L/R is the time constant used to establish the short-circuit.

In practice, after a time t = 3τ the short-circuit is considered to be established, because the value of exp(-3) = 0.05 is negligible compared to 1.The lower the corresponding time constant (e.g. battery circuit), the faster a short-circuit is established.

L/R Description DC applications2 ms Very fast short-circuit b Photovoltaic applications5 ms Fast short-circuit established b Resistive or slightly inductive circuits:

v indicator light v trip units (MN, MX) v motor armatures v battery charger/uninterruptible power supply

(UPS) b Capacitive circuits: electronic controller

15 ms Standardised value used in standard IEC 60947-2

b Inductive circuits: v electromagnetic coil v contactor coil v motor inductor

30 ms Slower short-circuit established

b Highly inductive circuits: v electromagnetic coil v contactor coil v motor inductor

In general, the system time constant is calculated under worst case conditions, across the terminals of the generator.


R L

Isc

95

63

40

τt

2τ 3τ 4τ

% Isc

Isc

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DB

1242

45D

B12

4246

8



Tripping curvesWe can choose our solution according to the inrush currents generated by our loads, in the same way as for alternating current. In direct current, the same thermal tripping curves are obtained as in alternating current. The only difference is that the magnetic thresholds are offset by a coefficient √2 compared to the curves obtained in alternating current.

Characteristics of the various curves and their applications:

Curves Magnetic thresholds DC applications AC DC

Z 2.4 to 3.6 In 3.4 to 5 In b Resistive loads b Loads with electronic circuits

B 3.2 to 4.8 In 4.5 to 6.8 In b Motor inductor: starting current 2 to 4 In b Battery charger/Uninterruptible power supply

(UPS)C 6.4 to 9.6 In 9.05 to 13.6 In b Electronic controllerD et K 9.6 to 14.4 In 13.6 to 20.4 In b Electromagnetic coil: inrush overvoltage

10 to 20 Un b LV relay b Trip units (MN, MX) b Indicator light b PLCs (industrial programmable

logic controllers)

The figures opposite are iC60 tripping curves showing DC magnetic thresholds and normative limits

ExampleProtection of the 4 mm2 cable supplying a load at In = 30 A with a 32 A rating and a tripping curve that allows the starting current for this load to be absorbed.

DB

1241

88

t(s)

0,01

0,1

1

10

100

1000

I / In

B C D

15.7±20% 11.3±20% 17±20%

3600 s for I/In = 1.3

3600 sforI/In = 1.05

Curves B, C, D, ratings 6 A to 63 A

DB

1242

44

t(s)

0,01

0,1

1

10

100

1000

I (A)100 100010

4 mm2 cable fusion curve

Startingcurrent

iC60, 32 A C curve

Curve C, rating 32 A (AC magnetic thresholds in dotted lines)

DB

1244

51

I / In

t(s)

0,01

0,1

1

10

100

1000

KZ

14.2±20% 17±20%

3600 s for I/In = 1.33600 sforI/In = 1.05

Curves Z, K, ratings 6 A to 63 A

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Total discrimination: 10 kAUpstream Curve C Time constant (L/R) = 15 msiC60a C120N NSX

In (A) 10 - 16 20 - 25 32 40 50 - 63 80 100 125 u 100Downstream

iC60aCurves B,C

y 3 T T T T T T T T T4 T T T T T T T T6 T T T T T T T10 T T T T T13 T T T T T16 to 25 T T T T32 T T T T40 T T T50 - 63 T T

T Total discrimination.

No discrimination.

Continuity of service of the solutions Discrimination of the direct current protection devices Discrimination is a key element that must be taken into account right from the design stage of a low-voltage installation to allow continuity of service of the electrical power.

Discrimination involves coordination between two circuit breakers connected in series, so that in the event of a fault, only the circuit breaker positioned immediately upstream of the fault trips. A discrimination current Is is defined as:

b I fault < Is: only D2 removes the fault, discrimination ensured, b I fault > Is: both circuit breakers may trip, discrimination not ensured.

Discrimination may be partial or total, up to the breaking capacity of the downstream circuit breaker. To ensure total discrimination, the characteristics of the upstream device must be higher than those of the downstream one.

The same principles apply to designing both direct current and alternating current installations. Only the limit currents change when direct current is used.

Once again, we find the same concepts of discrimination: b total: up to the breaking capacity of the downstream device. Our tests have been

performed at up to 25 kA or 50 kA depending on the breaking capacity of the devices in question.

b partial: indication of the discrimination limit current Is. Discrimination is ensured below this value; above this value, the upstream device participates in the breaking process,

b none: no discrimination ensured, the upstream and downstream circuit breakers will trip.

For further information about the discrimination concept for protection devices in general, refer to technical supplement 557E4300, "Discrimination of modular circuit breakers".

Total discrimination solutionsIn the following tables, we offer you solutions that favour continuity of service (total discrimination between circuit breakers), for different short-circuit currents.

Only D2 trips D1 and D2 trip

Ifault0 D2 Is

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DB

1242

48D

B12

4247

10



Total discrimination: 15 kAUpstream Curve C Time constant (L/R) = 15 msiC60N C120N NSX

In (A) 10 - 16 20 - 25 32 40 50 - 63 80 100 125 u 100Downstream

iC60NCurves B,C

y 3 T T T T T T T T T4 T T T T T T T T6 T T T T T T10 T T T T T13 T T T T16 to 25 T T T T32 T T T40 T T T50 - 63 T T

Total discrimination: 20 kAUpstream Curve C Time constant (L/R) = 15 msiC60H C120H NSX

In (A) 10 - 16 20 - 25 32 40 50 - 63 80 100 125 u 100Downstream

iC60HCurves B,C

y 3 T T T T T T T T T4 T T T T T T T T6 T T T T T T10 T T T T13 T T T T16 to 25 T T T T32 T T T40 T T50 - 63 T T

Total discrimination: 25 kAUpstream Curve C Time constant (L/R) = 15 msiC60L NG125N NSX

In (A) 10 - 16 20 - 25 32 40 50 - 63 80 100 125 u 100Downstream

iC60LCurves B,C

y 3 T T T T T T T T T4 T T T T T T T T6 T T T T T T10 T T T T13 T T T T16 to 25 T T T T32 T T40 T T50 - 63 T

Total discrimination: 36 kAUpstream Curve C Time constant (L/R) = 15 msNG125H NSX

In (A) 80 u 100Downstream

NG125HCurves B,C

10 T T16 to 63 T

Total discrimination: 50 kAUpstream Curve C Time constant (L/R) = 15 msNG125L NSX

In (A) 80 u 100Downstream

NG125LCurves B,C

10 T T16 to 63 T

T Total discrimination.

No discrimination.

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DB

1242

51

DB

1242

49

Coordination with loads As seen above, the circuit-breaker characteristics chosen depend on the type of load downstream of the installation.The rating depends on the size of the cables to be protected and the curves depend on the load inrush current. Product selection according to the load inrush current When certain "capacitive" loads are switched on, very high inrush currents appear during the first milliseconds of operation. The following graphs show the average DC non-tripping curves of our products for this time range (50 μs to 10 ms).

iC60

DB

1242

49

Ipeak/In

t(ms)

0,01

0,1

1

10

100 1000101

Curve DCurve B

Curve C

NG125 / C120

DB

1242

50

t(ms)

0,01

0,1

1

10

100 1000101Ipeak/In

Curve DCurve B

Curve C

This information allows us to select the most appropriate product, according to the load specifications: curve and rating.

ExampleWhen an iC60 is used with a load with current peaks in the order of 200 In during the first 0.1 millisecond, a curve C or D product must be installed.

Ipeak/In

t(ms)

0,01

0,1

1

10

100 1000101

Curve DCurve B

Curve C

0,1

100 200 1000

0,1

200

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Personal protectionPersonal protection (earth-leakage protection) is not mandatory for this voltage range (24-48 V DC).In fact, according to the standards currently in force, the minimum ventricular fibrillation current If for human beings is in the order of 25 mA for alternating current (50 Hz), whereas for direct current, it is more than 50 mA. The table below shows the data according to the standards and conditions:

Environment Voltage specificationsAC DC

Dry environmentZman = 2000 Ohm

Uf = Z x If 50 V 100 V

Wet environmentZman = 1000 Ohm

Uf = Z x If 25 V 50 V

With Z corresponding to the impedance of the human body in the different types of environment, If being the current passing through the body and Uf the minimum contact voltage required to reach the danger current.

Under normal operating conditions, this voltage range (< 50 V) is therefore not dangerous to human beings.

DB

1242

38D

B12

4239

DB

1242

37

UfIf

Zman

Standards: IEC 60479-2, NF C 15100, IEC 60755.

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Examples of applicationsIndustrial applicationsMonitoring of agro-food tanks with 24 V DC converters for probes and other sensors

b Isolated network: v Isc = 25 kA, v In = 40 A.

SolutioniC60L 2P 40 A + 24 V converters

DB

1242

58InUn

Tank 1 probe

Tank 2 probe

Tank 3 probe

Tank 4 probe

Isc

Control of industrial process measurement by 12/24/48 V DC control b Isolated network: v Isc = 20 kA, v In = 40 A.

SolutioniC60H 2P 40 A + DC solid-state relays

DB

1242

61

InUn

Isc

Load 1 Load 2 Load 3

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24 V DC generator power supply protection b Earthed network: v Isc = 10 kA / In = 63 A, v Isc = 10 kA / In = 20 A.

SolutioniC60N 2P 63 A + iC60N 2P 20 A + DC loads

DB

1242

62

In1

In2

Isc1

AC network

Load 1

Isc2

DC network

Load 2 Load 3

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Tertiary applicationsControl and monitoring of the 48 V DC emergency lighting distribution for a shopping centre

b Mid-point of the network: v Isc = 20 kA, v In = 125 A.

SolutionNG125H 3P 125 A + power contactors

DB

1242

59

Un/2

Un/2In

Isc

Shopping centre lighting Zone 1




Major airport in France, 48 V DC emergency lighting for runways b Isolated network: v Isc = 50 kA, v In = 80 A.

SolutionNG125L 2P 80 A + impulse relays

DB

1242

60

InUn

Runway 1 lighting

IscIscRunway 2 lighting

Runway 3 lighting

Runway 4 lighting

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Power supply protection by 24 V DC direct current generator b Earthed network: v Isc1 = 10 kA / In = 40 A, v Isc2 = 10 kA / In = 2/4/6 A.

SolutioniC60N 2P 40 A + iC60N 2P 2/4/6 A + PLC inputs + DC loads

The Phaseo network failure solution provides the installation (or part thereof) with a 24 V DC power supply in the event of a mains voltage failure:

b throughout the mains failure, to ensure the continuity of service of the installation. b during a limited time to allow: v data to be backed up, v actuators to be put in the fallback position, v a generating set to be started up, v the operating systems to be shut down, v remote supervision data to be transmitted.

DB

1242

82

In1

In2

+

AC network

DC network

Load 1Input 1 Input 2

PLC

Input 3 Load 2

Isc1

Isc2

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Schneider Electric Industries SASAs standards, specifications and designs change from time to time, please ask for confirmation of the information given in this publication.

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1.5 4/10/2013 Changed NS by NSX and photos Sedoc1.4 5/04/2013 Replace I by In and U by Un Sedoc1.3 29/05/2012 Changed solution diagrams page 4 and 5 Sedoc1.2 21/09/2011 Changed solution diagrams page 4 and 5. Add 2 ms line in table page 7 Sedoc1.1 24/08/2011 Changed content page 2 - texts page 3, 4, 9 - Z, K curves page 8 Sedoc1.0 21/04/2011 Creation SedocIndice Date Modification Name

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circuit breakers for direct current applications

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